This invention relates to a process for removing heavy metal pollutants from aqueous solutions by precipitation. In U.S. Pat. No. 3,740,331 Anderson et al. describe a method of removing heavy metal pollutants from aqueous solutions. According to said invention, a metal ion such as ferrous that will form a sulfide having a higher equlibrium sulfide ion concentration than the sulfide of the heavy metal pollutant is added to the aqueous solution to form a sulfide precipitate of the pollutant heavy metal. A soluble salt of the heavy metal to be added is dissolved in the solution before the sulfide ion is introduced. The added heavy metal ion then acts as an excess sulfide scavenger when sulfide is added to precipitate the less soluble sulfide and prevents the generation of noxious quantities of hydrogen sulfide and formation of complexes of soluble sulfide ions. In practicing said invention it has been found that although precipitation of the pollutant heavy metal sulfide is substantially quantitatively complete, the formation of colloidal and very finely divided heavy metal sulfides can occur by this method. These finely precipitated and colloidal sulfides make it difficult to separate the precipitated metal from the treated solution by sedimentation and filtration processes.